The inventive concept relates generally to circuits generating one or more clock signals, and more particularly to a voltage-controlled oscillator and a phase-locked loop having the voltage-controlled oscillator.
Voltage-controlled oscillators (VCOs) in many different forms generate an oscillating output voltage. VCOs are widely used in analog and digital circuits. In common exemplary applications, VCOs are used in phase-locked loop (PLL) circuits, clock generation circuits, and data communication devices recovering clock and data signals.
PLL circuits are widely used in memory devices to generate various clock signals. Recent design trends for contemporary memory devices have reduced the level of many operating voltages within the memory devices. At the same time, clock signals of increasing frequency are used within memory devices to provide expanded data throughput (or bandwidth). These two design objectives are at odds, since increased voltage levels have historically accompanied demands for increased operating clock frequency. Thus, contemporary design goals seek to provide clock signals having a range of operating frequencies at relatively low operating voltages. Frequency, signal timing, and phase coherency requirements (e.g., same frequency and/or same phase) are also important in the generation of clock signals within memory devices and in the management of various internal and external clock signals.